1,2,2,2-tetrafluoroethyl ethers, and liquid-crystalline medium

ABSTRACT

1,2,2,2-Tetrafluoroethyl ethers of the formula I 
     
         R--(A.sup.1 --Z.sup.1).sub.m --A.sup.2 --Z.sup.2 A.sup.3 
    
      --O--CHF--CF 3 (I) 
     are suitable as components of liquid-crystalline media wherein 
     R is H, a substituted or unsubstituted alkyl or alkenyl radical having 1 to 15 carbon atoms, 
     A 1  and A 2  are each, independently of one another, a 
     (a) trans-1,4-cyclohexylene radicals and derivatives thereof in which, in addition, one or more non-adjacent CH 2  groups is optionally replaced by --O-- and/or --S--, 
     (b) 1,4-phenylene radicals and derivatives thereof in which, in addition, one or two CH groups is optionally replaced by N, or 
     (c) radical from the group consisting of 1,4-cyclohexenylene, 1,4-bicyclo(2,2,2)octylene, piperidine-1,4-diyl, naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl and 1,2,3,4-tetrahydronaphthalene-2,6-diyl, 
     wherein radicals (a) and (b) are optionally substituted by one or two fluorine atoms, 
     Z 1  and Z 2  are each, independently of one another, --CO--O--, --O--CO--, --CH 2  O--, --OCH 2  --, --CH 2  CH 2  --, --CH═CH--, --C.tbd.C-- or a single bond, and one of the radicals Z 1  and Z 2  is optionally --(CH 2 ) 4  -- --CH═CH--CH 2  CH 2  --, 
     X is H, F or Cl and 
     is 0, 1 or 2.

This application is a 371 of PCT/EP94/00767 filed Mar. 11, 1994.

The invention relates to 1,2,2,2-tetrafluoroethyl ethers of the formulaI

    R--(A.sup.1 --Z.sup.1).sub.m --A.sup.2 --Z.sup.2 --A.sup.3 --O--CHF--CF.sub.3                                        I

in which

R is H, an alkyl or alkenyl radical having 1 to 15 carbon atoms which isunsubstituted, monosubstituted by CN or CF₃ or at least monosubstitutedby halogen, it also being possible for one or more CH₂ groups in theseradicals to be replaced, in each case independently of one another, by--O--, --S--, ##STR1## --CO--, --CO--O--, --O--CO-- or --O--CO--O-- insuch a way that O atoms are not linked directly to one another,

A¹, A²

and A³ are each, independently of one another,

(a) a trans-1,4-cyclohexylene radical in which, in addition, one or morenon-adjacent CH₂ groups can be replaced by --O-- and/or --S--,

(b) a 1,4-phenylene radical in which, in addition, one or two CH groupscan be replaced by N,

(c) a radical from the group consisting of 1,4-cyclohexenylene,1,4-bicyclo[2.2.2]octylene, piperidine-1,4-diyl, naphthalene-2,6-diyl,decahydronaphthalene-2,6-diyl and 1,2,3,4-tetrahydronaphtalene-2,6-diyl,

where the radicals (a) and (b) can be substituted by one or two fluorineatoms,

Z¹ and Z² are each, independently of one another, --CO--O--, --O--CO--,--CH₂ O--, --OCH₂ --, --CH₂ CH₂ --, --CH═CH--, --C.tbd.C-- or a singlebond, and one of the radicals Z¹ and Z² is alternatively --(CH₂)₄ -- or--CH═CH--CH₂ CH₂ --, and

m is 0, 1 or 2.

The invention furthermore relates to the use of these compounds ascomponents of liquid-crystalline media and to liquid-crystal andelectro-optical display elements containing the liquid-crystalline mediaaccording ing to the invention.

The compounds of the formula I can be used as components ofliquid-crystalline media, in particular for displays based on theprinciple of the twisted cell, the guest-host effect, the effect ofdeformation of aligned phases or the effect of dynamic scattering.

The invention had the object of finding novel, stable,liquid-crystalline or mesogenic compounds which are suitable ascomponents of liquid-crystalline media and in particular have at thesame time comparatively low viscosity and relatively high dielectricanisotropy.

It has now been found that compounds of the formula I are eminentlysuitable as components of liquid-crystalline media. In particular, theyhave comparatively low viscosities. They can be used to obtain stableliquid-crystalline media having a broad mesophase range and advantageousvalues for the optical and dielectric anisotropy. Furthermore, thesemedia have very good low-temperature behaviour.

In the general formula, WO 88/00335 covers the compounds of the formulaI, but the compounds according to the invention are not mentionedtherein.

DE-A 41 04 126 describes compounds containing a terminal O--CH₂ --CF₃ orO--CH₂ --CH₂ F group, such as, for example, ##STR2##

However, in view of the very wide range of areas of application of suchcompounds having high Δε, it was desirable to have available furthercompounds of high nematogeneity which have properties preciselycustomized to the particular applications.

In addition, the provision of compounds of the formula I very generallyconsiderably broadens the range of liquid-crystalline substances whichare suitable, from various applicational points of view, for thepreparation of liquid-crystalline mixtures.

The compounds of the formula I have a broad range of applications.Depending on the choice of substituents, these compounds can be used asbase materials from which liquid-crystalline media are predominantlycomposed; however, it is also possible to add compounds of the formula Ito liquid-crystalline base materials from other classes of compound inorder, for example, to modify the dielectric and/or optical anisotropyof a dielectric of this type and/or to optimize its threshold voltageand/or its viscosity.

In the pure state, the compounds of the formula I are colorless and formliquid-crystalline mesophases in a temperature range which is favourablylocated for electro-optical use. They are stable chemically, thermallyand to light.

The invention thus relates to the compounds of the formula I and to theuse of these compounds as components of liquid-crystalline media. Theinvention furthermore relates to liquid-crystalline media containing atleast one compound of the formula I and to liquid-crystal displayelements, in particular electro-optical display elements, containingmedia of this type.

For reasons of simplicity, A³ below is a radical of the formula ##STR3##where r is 0, 1 or 2, Y is O--CH--CF₃, Cyc denotes a 1,4-cyclohexylradical, Che denotes a 1,4-cyclohexenylene radical, Dio denotes a1,3-dioxane-2,5-diyl radical, Dit denotes a 1,3-dithiane-2,5 -diylradical, Phe denotes a 1,4-phenylene radical, Pyd denotes apyridine-2,5-diyl radical, Pyr denotes a pyrimidine-2,5-diyl radical andBi denotes a bicyclo-[2.2.2.]octylene radical, where Cyc and/or Phe canbe unsubstituted or monosubstituted or disubstituted by F or CN.

A¹, A² and A³ are preferably selected from the group consisting of Cyc,Che, Phe, PYr, Pyd and Dio, it being preferred that only one of theradicals A¹, A² and A³ present in the molecule is Che, Phe, Pyr, Pyd orDio.

Accordingly, the compounds of the formula I cover bicyclic compounds ofthe subformulae Ia and Ib:

    ______________________________________                                        R--A.sup.2 --A.sup.3 --Y Ia                                                   R--A.sup.2 --Z.sup.2 --A.sup.3 --Y                                                                     Ib                                                   ______________________________________                                    

tricyclic compounds of the subformulae Ic to If:

    ______________________________________                                        R--A.sup.1 --A.sup.2 --A.sup.3 --Y                                                                      Ic                                                  R--A.sup.1 --Z.sup.1 --A.sup.2 --Z.sup.2 --A.sup.3 --Y                                                  Id                                                  R--A.sup.1 --Z.sup.1 --A.sup.2 --A.sup.3 --Y                                                            Ie                                                  R--A.sup.1 --A.sup.2 --Z.sup.2 --A.sup.3 --Y                                                            If                                                  ______________________________________                                    

and tetracyclic compounds of the subformulae Ig to Im:

    ______________________________________                                        R--A.sup.1 --A.sup.1 --A.sup.2 --A.sup.3 --Y                                                              Ig                                                R--A.sup.1 --Z.sup.1 --A.sup.1 --A.sup.2 --A.sup.3 --Y                                                    Ih                                                R--A.sup.1 --A.sup.1 --Z.sup.1 --A.sup.2 --A.sup.3 --Y                                                    Ii                                                R--A.sup.1 --A.sup.1 --A.sup.2 --Z.sup.2 --A.sup.3 --Y                                                    Ij                                                R--A.sup.1 --Z.sup.1 --A.sup.1 --Z.sup.1 --A.sup.2 --A.sup.3 --Y                                          Ik                                                R--A.sup.1 --A.sup.1 --Z.sup.1 --A.sup.2 --Z.sup.2 --A.sup.3 --Y                                          Il                                                R--A.sup.1 --Z.sup.1 --A.sup.1 --Z.sup.1 --A.sup.2 --Z.sup.2 --A.sup.3        --Y                         Im                                                ______________________________________                                    

Of these, particular preference is given to the compounds of thesubformulae Ia, Ib, Ic, Id, Ie, If, Ii and Il.

Preferred compounds of the subformula Ia are those of the subformulaeIaa to Iaf:

    ______________________________________                                        R--Phe--A.sup.3 --Y     Iaa                                                   R--Dio--A.sup.3 --Y     Iab                                                   R--Pyr--A.sup.3 --Y     Iac                                                   R--Pyd--A.sup.3 --Y     Iad                                                   R--Cyc--A.sup.3 --Y     Iae                                                   R--Che--A.sup.3 --Y     Iaf                                                   ______________________________________                                    

Of these, those of the formulae Iaa and Iae are particularly preferred.

Preferred compounds of the subformula Ib are those of the subformulaeIba to Ibc:

    ______________________________________                                        R--Cyc--CH.sub.2 CH.sub.2 --A.sup.3 --Y                                                                Iba                                                  R--Cyc--COO--A.sup.3 --Y Ibb                                                  R--Phe--COO--A.sup.3 --Y Ibc                                                  ______________________________________                                    

Preferred compounds of the subformula Ic are those of the subformulaeIca to Icn:

    ______________________________________                                        R--Phe--Phe--A.sup.3 --Y                                                                              Ica                                                   R--Phe--Pyd--A.sup.3 --Y                                                                              Icb                                                   R--Phe--Dio--A.sup.3 --Y                                                                              Icc                                                   R--Cyc--Cyc--A.sup.3 --Y                                                                              Icd                                                   R--Phe--Cyc--A.sup.3 --Y                                                                              Ice                                                   R--Cyc--Pyd--A.sup.3 --Y                                                                              Icf                                                   R--Pyd--Phe--A.sup.3 --Y                                                                              Icg                                                   R--Pyr--Phe--A.sup.3 --Y                                                                              Ich                                                   R--Phe--Pyr--A.sup.3 --Y                                                                              Ici                                                   R--Cyc--Pyr--A.sup.3 --Y                                                                              Icj                                                   R--Cyc--Phe--A.sup.3 --Y                                                                              Ick                                                   R--Dio--Phe--A.sup.3 --Y                                                                              Icl                                                   R--Che--Phe--A.sup.3 --Y                                                                              Icm                                                   R--Phe--Che--A.sup.3 --Y                                                                              Icn                                                   ______________________________________                                    

Of these, those of the formulae Ica, Icd, Ice and Ick are particularlypreferred.

Preferred compounds of the subformula Ib are those of the subformulaeIda to Idk:

    ______________________________________                                        R--Phe--Z.sup.1 --Phe--Z.sup.2 --A.sup.3 --Y                                                            Ida                                                 R--Phe--Z.sup.1 --Dio--Z.sup.2 --A.sup.3 --Y                                                            Idb                                                 R--Cyc--Z.sup.1 --Cyc--Z.sup.2 --A.sup.3 --Y                                                            Idc                                                 R--Cyc--Z.sup.1 --Pyr--Z.sup.2 --A.sup.3 --Y                                                            Idd                                                 R--Pyd--Z.sup.1 --Phe--Z.sup.2 --A.sup.3 --Y                                                            Ide                                                 R--Phe--Z.sup.1 --Pyd--Z.sup.2 --A.sup.3 --Y                                                            Idf                                                 R--Pyr--Z.sup.1 --Phe--Z.sup.2 --A.sup.3 --Y                                                            Idg                                                 R--Phe--Z.sup.1 --Pyr--Z.sup.2 --A.sup.3 --Y                                                            Idh                                                 R--Phe--Z.sup.1 --Cyc--Z.sup.2 --A.sup.3 --Y                                                            Idi                                                 R--Cyc--Z.sup.1 --Phe--Z.sup.2 --A.sup.3 --Y                                                            Idj                                                 R--Dio--Z.sup.1 --Phe--Z.sup.2 --A.sup.3 --Y                                                            Idk                                                 ______________________________________                                    

Preferred compounds of the subformula Ie are those of the subformulaeIea to Iej:

    ______________________________________                                        R--Pyr--Z.sup.1 --Phe--A.sup.3 --Y                                                                     Iea                                                  R--Dio--Z.sup.1 --Phe--A.sup.3 --Y                                                                     Ieb                                                  R--Phe--Z.sup.1 --Phe--A.sup.3 --Y                                                                     Iec                                                  R--Cyc--Z.sup.1 --Phe--A.sup.3 --Y                                                                     Ied                                                  R--Phe--Z.sup.1 --Cyc--A.sup.3 --Y                                                                     Iee                                                  R--Cyc--Z.sup.1 --Cyc--A.sup.3 --Y                                                                     Ief                                                  R--Phe--Z.sup.1 --Dio--A.sup.3 --Y                                                                     Ieg                                                  R--Pyd--Z.sup.1 --Phe--A.sup.3 --Y                                                                     Ieh                                                  R--Phe--Z.sup.1 --Pyr--A.sup.3 --Y                                                                     Iei                                                  R--Cyc--Z.sup.1 --Pyr--A.sup.3 --Y                                                                     Iej                                                  ______________________________________                                    

Preferred compounds of the sub formula If are those of the subformulaeIfa to Ifn:

    ______________________________________                                        R--Pyr--Phe--Z.sup.2 --A.sup.3 --Y                                                                      Ifa                                                 R--Pyr--Phe--OCH.sub.2 --A.sup.3 --Y                                                                    Ifb                                                 R--Phe--Phe--Z.sup.2 --A.sup.3 --Y                                                                      Ifc                                                 R--Phe--Phe--OOC--A.sup.3 --Y                                                                           Ifd                                                 R--Cyc--Cyc--Z.sup.2 --A.sup.3 --Y                                                                      Ife                                                 R--Cyc--Cyc--CH.sub.2 CH.sub.2 --A.sup.3 --Y                                                            Iff                                                 R--Pyd--Phe--Z.sup.2 --A.sup.3 --Y                                                                      Ifg                                                 R--Dio--Phe--Z.sup.2 --A.sup.3 --Y                                                                      Ifh                                                 R--Phe--Cyc--Z.sup.2 --A.sup.3 --Y                                                                      Ifi                                                 R--Phe--Pyd--Z.sup.2 --A.sup.3 --Y                                                                      Ifj                                                 R--Che--Phe--Z.sup.2 --A.sup.3 --Y                                                                      Ifk                                                 R--Phe--Che--Z.sup.2 --A.sup.3 --Y                                                                      Ifl                                                 R--Cyc--Phe--Z.sup.2 --A.sup.3 --Y                                                                      Ifm                                                 R--Cyc--Phe--OOC--A.sup.3 --Y                                                                           Ifn                                                 ______________________________________                                    

Preference is also given to compounds of the formula I and of allsubformulae in which A¹, A² and/or A³ is 1,4-phenylene which ismonosubstituted or disubstituted ed by F or monosubstituted by CN. Theseare, in particular, 2-fluoro-1,4-phenylene, 3-fluoro-1,4-phenylene and3,5-difluoro-1,4-phenylene and also 2-cyano-1,4-phenylene and3-cyano-1,4-phenylene. ##STR4##

Z¹ and Z² are preferably a single bond, --CO--O--, --O--CO-- or --CH₂CH₂ --, secondarily preferably --CH₂ O-- or --OCH₂ --.

If one of the radicals Z¹ and Z² is --(CH₂)₄ -- or --CH═CH--CH₂ CH₂ --,the other radical Z¹ or Z² (if present) is preferably a single bond.

Preferred compounds of this type conform to the subformula I' ##STR5##in which Z² is --(CH₂)₄ -- or --CH═CH--CH₂ CH₂ --, and R, A¹, A² and mare as defined under the formula I, and L² is H or F. The preferredmeanings of R, A¹, A² and m also correspond to those for the compoundsof the formula I.

m is preferably 1 or 0, particularly preferably 0.

If R is an alkyl radical and/or an alkoxy radical, this may bestraight-chain or branched. It is preferably straight-chain, has 2, 3,4, 5, 6 or 7 carbon atoms and accordingly is preferably ethyl, propyl,butyl, pentyl, hexyl, heptyl, ethoxy, propoxy, butoxy, pentoxy, hexoxyor heptoxy, furthermore methyl, octyl, nonyl, decyl, undecyl, dodecyl,tridecyl, tetradecyl, pentadecyl, methoxy, octoxy, nonoxy, decoky,undecoxy, dodecoxy, tridecoxy or tetradecoxy.

Oxaalkyl is preferably straight-chain 2-oxapropyl (=methoxymethyl), 2-(=ethoxymethyl) or 3-oxabutyl (=2-methoxyethyl), 2-, 3- or 4-oxapentyl,2-, 3-, 4- or 5-oxaheyxl, 2-, 3-, 4-, 5- or 6-oxaheptyl, 2-, 3-, 4-, 5-,6- or 7-oxaoctyl, 2-, 3-, 4-, 5-, 6-, 7- or 8-oxanonyl, or 2-, 3-, 4-,5-, 6-, 7-, 8 - or 9-oxadecyl.

If R is an alkyl radical in which one CH₂ group has been replaced by--CH═CH--, this may be straight-chain or branched. It is preferablystraight-chain and has 2 to 10 carbon atoms. Accordingly it is inparticular vinyl, prop-1- or -2-enyl, but-1-, -2- or -3-enyl, pent-1-2-,-3- or -4-enyl, hex-1-, -2-, -3-, -4- or -5-enyl, hept-1-, -2-, -3-,-4-, -5- or -6-enyl, oct-1-, -2-, -3-, -4-, 5-, -6- or -7-enyl, non-1-,-2-, -3-, -4-, -5-, -6-, -7-or -8-enyl, or dec-1-, -2-, -3-, -4-, -5-,-6-, -7-, -8or -9-enyl.

If R is an alkyl radical in which one CH₂ group has been replaced by--O-- and one has been replaced by --CO--, these are preferablyadjacent. This thus contains one acyloxy group --CO--O-- or oneoxycarbonyl group --O--CO--. This is preferably straight-chain and has 2to 6 carbon atoms.

Accordingly it is in particular acetoxy, propionyloxy, butyryloxy,pentanoyloxy, hexanoyloxy, acetoxymethyl, propionyloxymethyl,butyryloxymethyl, pentanoyloxymethyl, 2-acetoxyethyl,2-propionyloxyethyl, 2-butyryloxyethyl, 3-acetoxy-propyl,3-propionyloxypropyl, 4-acetoxybutyl, methoxycarbonyl, ethoxycarbonyl,propoxycarbonyl, butoxycarbonyl, pentoxycarbonyl, methoxycarbonylmethyl,ethoxycarbonylmethyl, propoxycarbonylmethyl, butoxycarbonylmethyl,2-(methoxycarbonyl)ethyl, 2-(ethoxycarbonyl) ethyl,2-(propoxycarbonyl)ethyl, 3-(methoxycarbonyl)propyl, 3-(ethoxycarbonyl )propyl or 4-(methoxycarbonyl)butyl.

If R is an alkyl radical in which one CH₂ group has been replaced byunsubstituted or substituted --CH═CH-- and an adjacent CH₂ group hasbeen replaced by CO or CO--O or O--CO--, this may be straight-chain orbranched. It is preferably straight-chain and has 4 to 13 carbon atoms.Accordingly it is in particular acryloyloxmethyl, 2-acryloyloxyethyl,3-acryloyl-oxypropyl, 4-acryloyloxybutyl, 5-acryloyloxypentyl,6-acryloyloxyhexyl, 7-acryloyloxygeptyl, 8-acryloyl-oxyoctyl,9-acryloyloxynonyl, 10-acryloyloxydecyl, methacryl oyloxymethyl,2-methacryloyloxyethyl, 3-meth-acryloyloxypropyl,4-methacryloyloxybutyl, 5-meth-acryloyloxypentyl,6-methacryloyloxyhexyl, 7-meth-acryloyloxyheptyl, 8-methacryloyloxyoctylor 9-meth-acryloyloxynonyl.

If R is an alkyl or alkenyl radical which is monosubstituted by CN orCF₃, this radical is preferably straight-chain and the substitution byCN or CF₃ is in the ω-position.

If R is an alkyl or alkenyl radical which is at least monosubstituted byhalogen, this radical is preferably ably straight-chain and halogen ispreferably. F or Cl. In the case of multiple substitution, halogen ispreferably F. The resulting radicals also include perfluorinatedradicals. In the case of monosubstitution, the fluorine or chlorinesubstituent can be in any desired position, but is preferably in theω-position.

Compounds of the formula I which contain wing groups R which aresuitable for polymerization reactions are suitable for the preparationof liquid-crystalline polymers.

Compounds of the formula I containing branched wing groups R mayoccasionally be of importance due to better solubility in the customaryliquid-crystalline base materials, but in particular as chiral dopes ifthey are optically active. Smectic compounds of this type are suitableas components of ferroelectric materials.

Compounds of the formula I having S_(A) phases are suitable, forexample, for thermally addressed displays.

Branched groups of this type generally contain not more than one chainbranch. Preferred branched radicals R are isopropyl, 2-butyl(=1-methylpropyl), isobutyl (=2-methylpropyl), 2-methylbutyl, isopentyl(=3-methylbutoxy), 2-methylpentyl, 3-methylpentyl, 2-ethylhexyl,2-propylpentyl, isopropoxy, 2-methyl -propoxy, 2-methylbutoxy,3-methylbutoxy, 2-methyl-pentoxy, 3-methylpentoxy, 2-ethylhexoxy, 1-methylhexoxy and 1-methylheptoxy.

If R is an alkyl radical in which two or more CH₂ groups have beenreplaced by --O-- and/or --CO--O--, this may be straight-chain orbranched. It is preferably branched and has 3 to 12 carbon atoms.Accordingly it is in particular biscarboxymethyl, 2,2-biscarboxyethyl,3,3-biscarboxypropyl, 4,4-bis-carboxybutyl, 5,5-biscarboxypentyl,6,6-bis-carboxyhexyl, 7,7-biscarboxyheptyl, 8,8-biscarboxy-octyl,9,9-biscarboxynonyl, 10,10-biscarboxydecyl, bis(methoxycarbonyl)methyl,2,2-bis(methoxycarbonyl)ethyl, 3,3-bis(methoxycarbonyl)propyl,4,4-bis(-methoxycarbonyl)butyl, 5,5-bis(methoxy-carbonyl)pentyl,6,6-bis(methoxycarbonyl)hexyl, 7,7-bis(methoxycarbonyl)heptyl, eptyl,8,8-bis(methoxycarbonyl)-octyl, bis(ethoxycarbony-1) methyl,2,2-bis(ethoxy-carbonyl)ethyl, 3,3-bis(ethoxycarbonyl)propyl,4,4-bis(ethoxycarbonyl)butyl or 5,5-bis(ethoxycarbonyl)hexyl.

Compounds of the formula I which contain wing groups R which aresuitable for polycondensations are suitable for the preparation ofliquid-crystalline polycondensates.

The formula I covers the racemates of these compounds and the opticalantipodes, and mixtures thereof.

Of these compounds of the formula I and of the subformulae, preferenceis given to those in which at least one of the radicals present thereinhas one of the preferred meanings mentioned.

In the compounds of the formula I, preference is given to thestereoisomers in which the rings Cyc and Piperidine aretrans-1,4-disubstituted. Those of the abovementioned formulae whichcontain one or more groups Pyd, Pyr and/or Dio in each case include thetwo 2,5-positional isomers.

Preferred smaller groups of compounds are those of the subformulae I1 toI19: ##STR6##

The 1,4-cyclohexenylene group preferably has the following structures:##STR7##

The compounds of the formula I are prepared by methods known per se, asdescribed in the literature (for example in the standard works such asHouben-Weyl, Methoden der Organischen Chemie, Georg-Thieme-Verlag,Stuttgart), to be precise under reaction conditions which are known andsuitable for said reactions.

Use may also be made of variants which are known per se, but are notmentioned here in greater detail.

The novel compounds can be prepared, for example, by metalating acompound of the formula II ##STR8## in which R, A¹, A², Z¹, Z² and m areas defined above, and L¹ and L² are H or F, as shown in the reactionscheme below, and subsequently reacting the product with1,2,2,2-tetrafluoro-1-iodoethane: ##STR9##

The invention also relates to a process for the preparation ofsubstituted 1,2,2,2-tetrafluoroethoxybenzene from the correspondingphenoxide, which is characterized in that the phenoxide is reacted with1,2,2,2-tetrafluoro-1-iodoethane in the presence of an inert solvent. Inparticular, the novel process can be used for the preparation ofcompounds of the formula III*. In the compounds of the formula III*, R*is halogen, formyl or a mesogenic group.

The reaction is carried out in the presence of an inert solvent,suitable solvents being the conventional solvents for reactions ofphenoxides with alkyl halides, preferably polar aprotic solvents, inparticular organic amides, such as, for example, dimethylamide (DMA),hexamethylphosphoric triamide (HMPTA) or N-methylpyrrolidone (NMP), orcyclic urea derivatives, such as, for example, N,N-dimethylpropyleneurea(DMPU) and in particular 1,3-dimethyl-2-imidazolidinone (DMEU).

It is also possible to add cosolvents, such as TMEDA or crown ethers,such as 18-crown-6, to these solvents. The amount of solvent is notcrucial; in general, from 100 to 10,000 g of solvent per mole ofphenoxide can be used.

The reaction in the novel process is simple to carry out, it beingpossible for the starting materials to be reacted, depending on thephenoxide used, at temperatures of from -20° to +200° C., preferably atfrom -20° to +150° C., and at superatmospheric pressure or reducedpressure, preferably at atmospheric pressure.

In an expedient procedure, the phenoxide is introduced into the reactorin an inert solvent and is warmed. 1,2,2,2-Tetrafluoro-1-iodoethane isadded dropwise with stirring, generally over the course of from 0.2 to24 hours, at from -20° C. to 100° C., and, if appropriate, the mixtureis allowed to warm slowly to the boiling point of the solvent.

In general, from 0.8 to 1.5 mol, preferably from 0.9 to 1.2 mol, of1,2,2,2-tetrafluoro-1-iodoethane are required per mole of the phenoxideto be reacted.

The reaction mixture is worked up and the products isolated in aconventional manner, for example by pouring the reaction mixture intowater and/or ice or dilute acid and, after separating off the aqueousphase, isolating the 1,2,2,2-tetrafluoroethoxybenzene derivatives bydistillation and/or crystallization.

Surprisingly, the novel process allows substituted1,2,2,2-tetrafluoroethoxybenzene derivatives, which are valuableintermediates, for example for liquid crystals, auxiliaries,plant-protection agents pharmaceuticals, to be prepared in a simplermanner than in the prior art and in higher yields.

The compounds of the formula II can be prepared, for example, as shownin the synthesis schemes below: ##STR10##

The starting materials are either known or can be prepared analogouslyto known compounds.

Esters of the formula I can also be obtained by esterification ofcorresponding carboxylic acids (or reactive derivatives thereof) usingalcohols or phenols (or reactive derivatives thereof) or by the DCCmethod (DCC=dicyclohexylcarbodiimide).

The corresponding carboxylic acids and alcohols or phenols are known orcan be prepared analogously to known processes.

In a further process for the preparation of the compounds of the formulaI, an aryl halide is reacted with an olefin in the presence of atertiary amine and in the presence of a palladium catalyst (cf. R. F.Heck, Acc. Chem. Res. 12(1979) 146). Examples of suitable aryl halidesare chlorides, bromides and iodides, in particular bromides and iodides.The tertiary amines which are necessary for the success of the couplingreaction, such as, for example, triethylamine, are also suitable assolvent. Examples of suitable palladium catalysts are palladium salts,in particular Pd(II) acetate, with organophosphorus(III) compounds, suchas, for example, triarylphosphines. The reaction can be carried out inthe presence or absence of an inert solvent at temperatures betweenabout 0° and 150°, preferably between 20° and 100°; suitable solventsare, for example, nitriles, such as acetonitrile, or hydrocarbons, suchas benzene or toluene. The aryl halides and olefins employed as startingmaterials are frequently commercially available or can be prepared byprocesses known from the literature, for example by halogenation ofcorresponding parent compounds or by elimination reactions oncorresponding alcohols or halides.

Stilbene derivatives, for example, can be prepared in this way. Thestilbenes can also be prepared by reacting a 4-substituted benzaldehydewith a corresponding phosphorus ylide by the Wittig method. However,tolans of the formula I can also be prepared by employingmonosubstituted acetylene instead of the olefin (Synthesis 627 (1980) orTetrahedron Lett. 27, 1171 (1986)).

Aromatic compounds can also be coupled by reacting aryl halides witharyltin compounds. These reactions are preferably carried out withaddition of a catalyst, such as, for example, a palladium(O)complex, ininert solvents, such as hydrocarbons, at high temperatures, for examplein boiling xylene under a protective gas.

Coupling reactions of alkynyl compounds with aryl halides can be carriedout analogously to the process described by A. O. King, E. Negishi, F.J. Villani and A. Silveira in J. Org. Chem. 43, 358 (1978).

Tolans of the formula I can also be prepared byFritsch-Buttenberg-Wiechell rearrangement (Ann. 279, 319, 1984), inwhich 1,1-diaryl-2-haloethylenes are rearranged in the presence ofstrong bases to give diarylacetylenes.

Tolans of the formula I can also be prepared by brominating thecorresponding stilbenes and then dehydrohalogenating the product. Usecan also be made here of variants of this reaction which are notmentioned in greater detail.

Ethers of the formula I are obtainable by etherification ofcorresponding hydroxyl compounds, preferably corresponding phenols, thehydroxyl compound expediently first being converted into a correspondingmetal derivative, for example into the corresponding alkali metalalkoxide or alkali metal phenoxide by treatment with NaH, NaNH₂, NaOH,KOH, Na₂ CO₃ or K₂ CO₃. This metal derivative can then be reacted withthe appropriate alkyl halide, alkyl sulphonate or dialkyl sulphonate,expediently in an inert solvent, such as, for example, acetone,1,2-dimethoxyethane, DMF or dimethyl sulphoxide or alternatively with anexcess of aqueous or aqueous-alcoholic NaOH or KOH at temperaturesbetween about 20° and 100° C.

The starting materials are either known or can be prepared analogouslyto known compounds.

The compounds of the formula I' in which Z² =--(CH₂)₄ -- can be preparedas shown in the following scheme: ##STR11##

The Pd(II)-catalyzed coupling reaction either forms the target productI' directly or forms a precursor, into which the radical --Y isintroduced completely analogously to the abovementioned methods forcompounds of the formula I.

The compounds of the formula I' in which Z² =--CH═CH--CH₂ CH₂ -- can beprepared by the Wittig method as shown in the following scheme:##STR12##

The preferred trans-isomers can be prepared by the isomerization methodsknown from the literature. Any intermediates obtained in which R°=H areconverted into the compounds of the formula I' entirely analogously tothe precursors of the compounds of the formula I by introduction of theradical --Y.

The aldehydes can be obtained by Heck reaction of appropriatelysubstituted 1-bromo-3-fluorobenzene derivatives with allyl alcohol.

The synthesis of some particularly preferred compounds is shown ingreater detail below: ##STR13##

The liquid-crystalline media according to the invention preferablycontain 2 to 40, in particular 4 to 30, components as furtherconstituents besides one or more compounds according to the invention.These media very particularly preferably contain 7 to 25 componentsbesides one or more compounds according to the invention. These furtherconstituents are preferably selected from nematic or nematogenic(monotropic or isotropic) substances stances, in particular substancesfrom the classes of the azoxybenzenes, benzylideneanilines, biphenyls,terphenyls, phenyl or cyclohexyl benzoates, phenyl or cyclohexyl estersof cyclohexanecarboxylic acid, phenyl or cyclohexyl esters ofcyclohexylbenzoic acid, phenyl or cyclohexylesters ofcyclohexylcyclohexanecarboxylic acid, cyclohexylphenyl esters of benzoicacid, of cyclohexanecarboxylic acid and ofcyclohexylcyclo-hexanecarboxylic acid, phenylcyclohexanes,cyclohexylbiphenyls, phenylcyclohexylcyclohexanes,cyclohexylcyclohexanes, cyclohexylcyclohexenes,1,4-bis-cyclohexylbenzenes, 4,4'-bis-cyclohexylbi-phenyls, phenyl- orcyclohexylpyrimidines, phenyl- or cyclo-hexylpyridines, phenyl- orcyclohexyldioxanes, phenyl- or cyclohexyl-1,3-dithianes,1,2-diphenyl-ethanes, 1,2-dicyclohexylethanes,1-phenyl-2-cyclo-hexylethanes,1-cyclohexyl-2-(4-phenyl-cyclohexyl)-ethanes,1-cyclohexyl-2-biphenylylethanes, 1-phenyl-2-cyclohexylphenylethanes,optionally halogenated stilbenes, benzyl phenyl ethers, tolans andsubstituted cinnamic acids. The 1,4-phenylene groups in these compoundsmay also be fluorinated.

The most important compounds suitable as further constituents of mediaaccording to the invention can be characterized by the formulae 1, 2, 3,4 and 5:

    ______________________________________                                        R'--L--E--R"        1                                                         R'--L--COO--E--R"   2                                                         R'--L--OOC--E--R"   3                                                         R'--L--CH.sub.2 CH.sub.2 --E--R"                                                                  4                                                         R'--L--C.sub.-- C--E--R"                                                                          5                                                         ______________________________________                                    

In the formulae 1, 2, 3, 4 and 5, L and E, which may be identical ordifferent, are in each case, independently of one another, a bivalentradical from the group formed by -Phe-, -Cyc-, -Phe-Phe-, -Phe-Cyc-,-Cyc-Cyc-, -Pyr-, -Dio-, -G-Phe- and -G-Cyc- and their mirror images,where Phe is unsubstituted or fluorine-substituted 1,4-phenylene, Cyc istrans-1,4-cyclo-hexylene or 1,4-cyclohexenylene, Pyr ispyrimidine-2,5-diyl or pyridine-2,5-diyl, Dio is 1,3-dioxane-2,5-diylend G is 2-(trans-1,4-cyclohexyl)ethyl, pyrimidine-2,5-diyl,pyridine-2,5-diyl or 1,3-dioxane-2,5-diyl.

One of the radicals L and E is preferably Cyc, Phe or Pyr. E ispreferably Cyc, Phe or Phe-Cyc. The media according to the inventionpreferably contain one or more components selected from the compounds ofthe formulae 1, 2, 3, 4 and 5 in which L and E are selected from thegroup consisting of Cyc, Phe and Pyr and simultaneously one or morecomponents selected from the compounds of the formulae 1, 2, 3, 4 and 5in which one of the radicals L and E is selected from the groupconsisting of Cyc, Phe and Pyr and the other radical is selected fromthe group consisting of -Phe-Phe-, -Phe-Cy-c-, -Cyc-Cyc-, -G-Phe- and-G-Cyc-, and optionally one or more components selected from thecompounds of the formulae 1, 2, 3, 4 and 5 in which the radicals L and Eare selected from the group consisting of -Phe-Cyc-, -Cyc-Cyc-, -G-Phe-and -G-Cyc-.

In a smaller sub-group of the compounds of the formulae 1, 2, 3, 4 and5, R' and R" are in each case, independently of one another, alkyl,alkenyl, alkoxy, alkoxyalkyl, alkenyloxy or alkanoyloxy having up to 8carbon atoms. This smaller sub-group is called group A below, and thecompounds are labelled with the sub-formulae 1a, 2a, 3a, 4a and 5a. Inmost of these compounds, R' and R" are different from one another, oneof these radicals usually being alkyl, alkenyl, alkoxy or alkoxyalkyl.

In another smaller sub-group of the compounds of the formulae 1, 2, 3, 4and 5 which is known as group B, R" is --F, --Cl, --NCS or --(O)_(i)CH₃₋(k+1) F_(k) Cl₁, where i 0 or 1, and k+1 is 1, 2 or 3; the compoundsin which R" has this meaning are labelled with the sub-formulae 1b, 2b,3b, 4b and 5b. Particular preference is given to those compounds of thesub-formulae 1b, 2b, 3b, 4b and 5b in which R" is --F, --Cl, --NCS,--CF₃, --OCHF₂ or --OCF₃.

In the compounds of the sub-formulae 1b, 2b, 3b, 4b and 5b, R' is asdefined for the compounds of the sub-formulae 1a-5a and is preferablyalkyl, alkenyl, alkoxy or alkoxyalkyl.

In a further smaller sub-group of the compounds of the formulae 1, 2, 3,4 and 5, R" is --CN; this subgroup is known as group C below, and thecompounds of this sub-group are correspondingly described bysub-formulae 1c, 2c, 3c, 4c and 5c. In the compounds of the sub-formulae1c, 2c, 3c, 4c and 5c, R' is as defined for the compounds of thesub-formulae la-Sa and is preferably alkyl, alkoxy or alkenyl.

In addition to the preferred compounds of groups A, B and C, othercompounds of the formulae 1, 2, 3, 4 and 5 having other variants of theproposed substituents are also customary. All these substances can beobtained by methods which are known from the literature or analogouslythereto.

Besides compounds of the formula I according to the invention, the mediaaccording to the invention preferably contain one or more compoundsselected from group A and/or group B and/or group C. The proportions byweight of the compounds from these groups in the media according to theinvention are preferably

Group A: 0 to 90%, preferably 20 to 90%, in particular 30 to 90%

Group B: 0 to 80%, preferably 10 to 80%, in particular 10 to 65%

Group C: 0 to 80%, preferably 5 to 80%, in particular 5 to 50%,

the sum of the proportions by weight of the group A and/or B and/or Ccompounds present in the particular media according to the inventionpreferably being 5 to 90% and in particular 10 to 90%.

The media according to the invention preferably contain 1 to 40%,particularly preferably 5 to 30%, of compounds according to theinvention. Further preferred media are those which contain more than40%, in particular 45 to 90%, of compounds according to the invention.The media preferably contain three, four or five compounds according tothe invention.

The media according to the invention are prepared in a manner which iscustomary per se. In general, the components are dissolved in oneanother, expediently at elevated temperature. By means of suitableadditives, the liquid-crystalline phases can be modified in accordancewith the invention in a manner such that they can be used in all typesof liquid-crystal display elements which have hitherto been disclosed.Additives of this type are known to those skilled in the art and aredescribed in detail in the literature (H. Kelker/R- Hatz, Handbook ofLiquid Crystals, Verlag Chemic, Weinheim, 1980). For example, pleochroicdyes can be added for the production of coloured guest-host systems, orsubstances can be added to modify the dielectric anisotropy, theviscosity and/or the alignment of the nematic phases.

In the present application and in the examples below, the structures ofthe liquid crystal compounds are indicated by acronyms, thetransformation into chemical formulae being carried out as shown inTables A and B below. All radicals C_(n) H_(2n+1) are straight-chainalkyl radicals having n carbon atoms. The coding in Table B isself-evident. In Table A, only the acronym for the parent structure isshown. In each individual case, the acronym for the parent structure isfollowed, separated by a hyphen, by a code for the substituents R¹, R² ,L¹ and L² :

    ______________________________________                                        Code for R.sup.1,                                                             R.sup.2, L.sup.1, L.sup.2                                                              R.sup.1         R.sup.2     L.sup.1                                                                           L.sup.2                              ______________________________________                                        nm       C.sub.n H.sub.2n+1                                                                            C.sub.m H.sub.2m+1                                                                        H   H                                    nOm      C.sub.n H.sub.2n+1                                                                            OC.sub.m H.sub.2m+1                                                                       H   H                                    nO.m     OC.sub.n H.sub.2n+1                                                                           C.sub.m H.sub.2m+1                                                                        H   H                                    n        C.sub.n H.sub.2n+1                                                                            CN          H   H                                    nN.F     C.sub.n H.sub.2n+1                                                                            CN          H   F                                    nF       C.sub.n H.sub.2n+1                                                                            F           H   H                                    nOF      OC.sub.n H.sub.2n+1                                                                           F           H   H                                    nCl      C.sub.n H.sub.2n+1                                                                            Cl          H   H                                    nF.F     C.sub.n H.sub.2n+1                                                                            F           H   F                                    nCF.sub.3                                                                              C.sub.n H.sub.2n+1                                                                            CF.sub.3    H   H                                    nOCF.sub.3                                                                             C.sub.n H.sub.2n+1                                                                            OCF.sub.3   H   H                                    nOCF.sub.2                                                                             C.sub.n H.sub.2n+1                                                                            OCHF.sub.2  H   H                                    nS       C.sub.n H.sub.2n+1                                                                            NCS         H   H                                    rVsN     C.sub.n H.sub.2n+1                                                                            CF.sub.3    H   H                                    nCF.sub.3                                                                              C.sub.r H.sub.2r+1 --CH═C.sub.s H.sub.2s --                                               CN          H   H                                    rEsN     C.sub.r H.sub.2r+1 --O--C.sub.s H.sub.2s --                                                   CN          H   H                                    nAm      C.sub.n H.sub.2n+1                                                                            COOC.sub.m H.sub.2m+1                                                                     H   H                                    nF.F.F   C.sub.n H.sub.2n+1                                                                            F           F   F                                    nCl.F.F. C.sub.n H.sub.2n+1                                                                            Cl          F   F                                    nCF.sub.3.F.F                                                                          C.sub.n H.sub.2n+1                                                                            CF.sub.3    F   F                                    nOCF.sub.3.F.F                                                                         C.sub.n H.sub.2n+1                                                                            OCF.sub.3   F   F                                    nOCF.sub.2.F.F                                                                         C.sub.n H.sub.2n+1                                                                            OCHF.sub.2  F   F                                    nOCF.sub.3.F                                                                           C.sub.n H.sub.2n+1                                                                            OCF.sub.3   F   H                                    ______________________________________                                         ##STR14##

The examples below are intended to illustrate the invention withoutrepresenting a limitation. Above and below, percentages are per cent byweight. All temperatures are given in degrees Celsius. m.p. denotesmelting point, c.p.=clearing point. Furthermore, C=crystalline state,N=nematic phase, S=smectic phase and I=isotophic phase. The numbersbetween these symbols represent the transition temperatures. An denotesoptical anisotropy (589 nm, 20° C.), and the viscosity (mm² / sec) wasdetermined at 20° C.

"Customary work-up" means that water is added if appropriate, themixture is extracted with dichloromethane, diethyl ether or toluene, thephases are separated, the organic phase is dried and evaporated, and theproduct is purified by distillation under reduced presssure orcrystallization and/or chromatography. The following abbreviations areused:

DAST diethylaminosulphur trifluoride

DMEU 1,3-dimethyl-2-imidazolidinone

POT potassium tertiary-butanolate

THF tetrahydrofuran

pTSOH p-toluenesulphonic acid

EXAMPLE 1 ##STR15##

Trifluoroacetaldehyde (prepared from 20 ml of conc. H₂ SO₄ and 0.17 molof CF₃ --CH(OH)₂) is passed at -50° C. into a solution comprising 0.1mol of trans-4-(trans-4-n-propylcyclohexyl) cyclohexanol in 200 ml ofdichloroethane. The mixture is stirred at -50° C. for 0.5 hour, and aspatula tip of potassium tert-butoxide is added to the mixture. Themixture is then stirred for a further 2 hours at -50° C. and allowed towarm to room temperature. The reaction mixture is evaporated andpurified by flash chromatography. ##STR16##

0.0756 mol of DAST is added dropwise at room temperature to 0.062 mol ofthe trifluorohydroxy ether from Example 1a) in 20 ml of dichloroethane.During the addition, the temperature of the reaction mixture should notexceed 30° C.

The mixture is stirred for 1 hour at room temperature and cooled to 0°C, and water is added in portions. The organic phase is separated offand subjected to conventional work-up. C 51 S_(B) (45) I, Δn=+0.034;Δε=7.08

The following compounds of the formula ##STR17## are obtainedanalogously:

    ______________________________________                                        R           (A.sup.1 Z.sup.1).sub.m A.sup.2 Z.sup.2                           ______________________________________                                        CH.sub.3                                                                                   ##STR18##                                                        C.sub.2 H.sub.5                                                                            ##STR19##                                                        n-C.sub.4 H.sub.9                                                                          ##STR20##                                                        n-C.sub.5 H.sub.11                                                                         ##STR21##                                                        n-C.sub.6 H.sub.13                                                                         ##STR22##                                                        n-C.sub.7 H.sub.15                                                                         ##STR23##                                                        CH.sub.3                                                                                   ##STR24##                                                        C.sub.2 H.sub.5                                                                            ##STR25##                                                        n-C.sub.3 H.sub.7                                                                          ##STR26##                                                        n-C.sub.4 H.sub.9                                                                          ##STR27##                                                        n-C.sub.5 H.sub.11                                                                         ##STR28##                                                        n-C.sub.6 H.sub.13                                                                         ##STR29##                                                        n-C.sub.7 H.sub.15                                                                         ##STR30##                                                        CH.sub.3                                                                                   ##STR31##                                                        C.sub.2 H.sub.5                                                                            ##STR32##                                                        n-C.sub.3 H.sub.7                                                                          ##STR33##                                                        n-C.sub.5 H.sub.11                                                                         ##STR34##                                                        n-C.sub.6 H.sub.13                                                                         ##STR35##                                                        CH.sub.3                                                                                   ##STR36##                                                        C.sub.2 H.sub.5                                                                            ##STR37##                                                        n-C.sub.3 H.sub.7                                                                          ##STR38##                                                        n-C.sub.5 H.sub.11                                                                         ##STR39##                                                        n-C.sub.6 H.sub.13                                                                         ##STR40##                                                        CH.sub.3                                                                                   ##STR41##                                                        C.sub.2 H.sub.5                                                                            ##STR42##                                                        n-C.sub.3 H.sub.7                                                                          ##STR43##                                                        n-C.sub.5 H.sub.11                                                                         ##STR44##                                                        n-C.sub.6 H.sub.13                                                                         ##STR45##                                                        CH.sub.3                                                                                   ##STR46##                                                        C.sub.2 H.sub.5                                                                            ##STR47##                                                        n-C.sub.3 H.sub.7                                                                          ##STR48##                                                        n-C.sub.5 H.sub.11                                                                         ##STR49##                                                        n-C.sub.6 H.sub.13                                                                         ##STR50##                                                        CH.sub.3                                                                                   ##STR51##                                                        C.sub.2 H.sub.5                                                                            ##STR52##                                                        n-C.sub.3 H.sub.7                                                                          ##STR53##                                                        n-C.sub.5 H.sub.11                                                                         ##STR54##                                                        n-C.sub.6 H.sub.13                                                                         ##STR55##                                                        CH.sub.3                                                                                   ##STR56##                                                        C.sub.2 H.sub.5                                                                            ##STR57##                                                        n-C.sub.3 H.sub.7                                                                          ##STR58##                                                        n-C.sub.5 H.sub.11                                                                         ##STR59##                                                        n-C.sub.6 H.sub.13                                                                         ##STR60##                                                        ______________________________________                                    

EXAMPLE 2 ##STR61## Step 2.1 ##STR62##

1.0 mol of sodium hydride (60%) is suspended in 200 ml of THF undernitrogen, and 1.0 mol of 4-bromo-2,6-difluorophenol, dissolved in 400 mlof THF, is added dropwise at 0° C. The mixture is allowed to warm toroom temperature, and is stirred for 0.5 hour and filtered. The filtrateis evaporated, dissolved in toluene and concentrated until crystalsform. The residue is precipitated using petroleum ether. The crystalsare filtered off with suction and dried.

Step 2.2 ##STR63##

0.08 mol of the phenoxide from 2.1 are introduced into 80 ml of DMEU,and the mixture is heated to 50° C. 0.088 mol of1,2,2,2-tetrafluoro-1-iodoethane is added, and the mixture is stirred at50° C. for 16 hours and allowed to cool to room temperature, and wateris added. The mixture is then acidified using dilute HCl and extractedwith methyl tert-butyl ether and then with 10% NaOH and water, and theextract is dried over Na₂ SO₄ and filtered. The filtrate is evaporateddistilled at 800 mbar in a bulb tube. b.p. 145° C.

Step 2.3 ##STR64##

0.013 mol of 4-[1,2,2,2-tetrafluoroethoxy]-2,6-difluorodibromobenzenedifluorodibromobenzene is dissolved in 50 ml of THF and heated to 60°C., and 0.012 mol of 4-(trans-4-propylcyclohexyl)-2,6-difluorophenylboronic acid and a solution comprising 0.013 mol ofKH₂ PO₄, 0.025 mol of Na₂ HPO₄ and 25 ml of water are added. 0.012 molof tetrakis[tri-phenylpalladium (0)] is added, and the mixture isstirred at 70° C. over night, allowed to cool to room temperature andsubjected to conventional work-up. C 104 I; Δn=+0.102; Δε=20.92.

The following compounds of the formula ##STR65## are preparedanalogously:

    ______________________________________                                        R      (A.sup.1 Z.sup.1).sub.m A.sup.2 Z.sup.2                                                              L.sup.1                                                                             L.sup.2                                   ______________________________________                                        C.sub.2 H.sub.5                                                                       ##STR66##             H     H                                         C.sub.2 H.sub.5                                                                       ##STR67##             F     H                                         C.sub.2 H.sub.5                                                                       ##STR68##             F     F                                         n-C.sub.3 H.sub.7                                                                     ##STR69##             H     H                                         n-C.sub.3 H.sub.7                                                                     ##STR70##             F     H                                         n-C.sub.5 H.sub.11                                                                    ##STR71##             H     H                                         n-C.sub.5 H.sub.11                                                                    ##STR72##             F     H                                         n-C.sub.5 H.sub.11                                                                    ##STR73##             F     F C 98I; Δε = 22.22;                                            Δn = +0.116                         n-C.sub.6 H.sub.13                                                                    ##STR74##             H     H                                         n-C.sub.6 H.sub.13                                                                    ##STR75##             F     H                                         n-C.sub.6 H.sub.13                                                                    ##STR76##             F     F                                         C.sub.2 H.sub.5                                                                       ##STR77##             H     H                                         C.sub.2 H.sub.5                                                                       ##STR78##             F     H                                         C.sub.2 H.sub.5                                                                       ##STR79##             F     F                                         n-C.sub.3 H.sub.7                                                                     ##STR80##             H     H                                         n-C.sub.3 H.sub.7                                                                     ##STR81##             F     H                                         n-C.sub.3 H.sub.7                                                                     ##STR82##             F     F                                         n-C.sub.5 H.sub.11                                                                    ##STR83##             H     H                                         n-C.sub.5 H.sub.11                                                                    ##STR84##             F     H                                         n-C.sub.5 H.sub.11                                                                    ##STR85##             F     F                                         C.sub.2 H.sub.5                                                                       ##STR86##             H     H                                         C.sub.2 H.sub.5                                                                       ##STR87##             H     F                                         C.sub.2 H.sub.5                                                                       ##STR88##             F     F                                         n-C.sub.3 H.sub.7                                                                     ##STR89##             H     H                                         n-C.sub.3 H.sub.7                                                                     ##STR90##             H     F                                         n-C.sub.3 H.sub.7                                                                     ##STR91##             F     F                                         n-C.sub.5 H.sub.11                                                                    ##STR92##             H     H                                         n-C.sub.5 H.sub.11                                                                    ##STR93##             H     F                                         n-C.sub.5 H.sub.11                                                                    ##STR94##             F     F                                         C.sub.2 H.sub.5                                                                       ##STR95##             H     H                                         C.sub.2 H.sub.5                                                                       ##STR96##             H     F                                         C.sub.2 H.sub.5                                                                       ##STR97##             F     F                                         n-C.sub.3 H.sub.7                                                                     ##STR98##             H     H                                         n-C.sub.3 H.sub.7                                                                     ##STR99##             H     F                                         n-C.sub.3 H.sub.7                                                                     ##STR100##            F     F                                         n-C.sub.5 H.sub.11                                                                    ##STR101##            H     H                                         n-C.sub.5 H.sub.11                                                                    ##STR102##            H     F                                         n-C.sub.5 H.sub.11                                                                    ##STR103##            F     F                                         C.sub.2 H.sub.5                                                                       ##STR104##            H     H                                         C.sub.2 H.sub.5                                                                       ##STR105##            H     F                                         C.sub.2 H.sub.5                                                                       ##STR106##            F     F                                         n-C.sub.3 H.sub.7                                                                     ##STR107##            H     H                                         n-C.sub.3 H.sub.7                                                                     ##STR108##            H     F                                         n-C.sub.3 H.sub.7                                                                     ##STR109##            F     F                                         n-C.sub.5 H.sub.11                                                                    ##STR110##            H     H                                         n-C.sub.5 H.sub.11                                                                    ##STR111##            H     F                                         n-C.sub.5 H.sub.11                                                                    ##STR112##            F     F                                         C.sub.2 H.sub.5                                                                       ##STR113##            H     H                                         C.sub.2 H.sub.5                                                                       ##STR114##            H     F                                         C.sub.2 H.sub.5                                                                       ##STR115##            F     F                                         n-C.sub.3 H.sub.7                                                                     ##STR116##            H     H                                         n-C.sub.3 H.sub.7                                                                     ##STR117##            H     F                                         n-C.sub.3 H.sub.7                                                                     ##STR118##            F     F                                         n-C.sub.5 H.sub.11                                                                    ##STR119##            H     H                                         n-C.sub.5 H.sub.11                                                                    ##STR120##            H     F                                         n-C.sub.5 H.sub.11                                                                    ##STR121##            F     F                                         C.sub.2 H.sub.5                                                                       ##STR122##            H     H                                         C.sub.2 H.sub.5                                                                       ##STR123##            H     F                                         C.sub.2 H.sub.5                                                                       ##STR124##            F     F                                         n-C.sub.3 H.sub.7                                                                     ##STR125##            H     H                                         n-C.sub.3 H.sub.7                                                                     ##STR126##            H     F                                         n-C.sub.3 H.sub.7                                                                     ##STR127##            F     F                                         n-C.sub.5 H.sub.11                                                                    ##STR128##            H     H                                         n-C.sub.5 H.sub.11                                                                    ##STR129##            H     F                                         n-C.sub.5 H.sub.11                                                                    ##STR130##            F     F                                         n-C.sub.3 H.sub.7                                                                     ##STR131##            H     H                                         n-C.sub.3 H.sub.7                                                                     ##STR132##            H     F                                         n-C.sub.3 H.sub.7                                                                     ##STR133##            F     F                                         n-C.sub.5 H.sub.11                                                                    ##STR134##            H     H                                         n-C.sub.5 H.sub.11                                                                    ##STR135##            H     F                                         n-C.sub.5 H.sub.11                                                                    ##STR136##            F     F                                         n-C.sub.3 H.sub.7                                                                     ##STR137##            H     H                                         n-C.sub.3 H.sub.7                                                                     ##STR138##            H     F                                         n-C.sub.3 H.sub.7                                                                     ##STR139##            F     F                                         n-C.sub.5 H.sub.11                                                                    ##STR140##            H     H                                         n-C.sub.5 H.sub.11                                                                    ##STR141##            H     F                                         n-C.sub.5 H.sub.11                                                                    ##STR142##            F     F                                         C.sub.2 H.sub.5                                                                       ##STR143##            H     H                                         C.sub.2 H.sub.5                                                                       ##STR144##            H     F                                         C.sub.2 H.sub.5                                                                       ##STR145##            F     F                                         n-C.sub.3 H.sub.7                                                                     ##STR146##            H     H                                         n-C.sub.3 H.sub.7                                                                     ##STR147##            H     F                                         n-C.sub.3 H.sub.7                                                                     ##STR148##            F     F                                         n-C.sub.5 H.sub.11                                                                    ##STR149##            H     H                                         n-C.sub.5 H.sub.11                                                                    ##STR150##            H     F                                         n-C.sub.5 H.sub.11                                                                    ##STR151##            F     F                                         C.sub.2 H.sub.5                                                                       ##STR152##            H     H                                         C.sub.2 H.sub.5                                                                       ##STR153##            H     F                                         C.sub.2 H.sub.5                                                                       ##STR154##            F     F                                         n-C.sub.3 H.sub.7                                                                     ##STR155##            H     H                                         n-C.sub.3 H.sub.7                                                                     ##STR156##            H     F                                         n-C.sub.3 H.sub.7                                                                     ##STR157##            F     F                                         n-C.sub.4 H.sub.9                                                                     ##STR158##            H     H                                         n-C.sub.4 H.sub.9                                                                     ##STR159##            H     F                                         n-C.sub.4 H.sub.9                                                                     ##STR160##            F     F                                         n-C.sub.5 H.sub.11                                                                    ##STR161##            H     H                                         n-C.sub.5 H.sub.11                                                                    ##STR162##            H     F                                         n-C.sub.5 H.sub.11                                                                    ##STR163##            F     F                                         C.sub.2 H.sub.5                                                                       ##STR164##            H     H                                         C.sub.2 H.sub.5                                                                       ##STR165##            H     F                                         C.sub.2 H.sub.5                                                                       ##STR166##            F     F                                         n-C.sub.3 H.sub.7                                                                     ##STR167##            H     H                                         n-C.sub.3 H.sub.7                                                                     ##STR168##            H     F                                         n-C.sub.3 H.sub.7                                                                     ##STR169##            F     F                                         n-C.sub.5 H.sub.11                                                                    ##STR170##            H     H                                         n-C.sub.5 H.sub.11                                                                    ##STR171##            H     F                                         n-C.sub.5 H.sub.11                                                                    ##STR172##            F     F                                         C.sub.2 H.sub.5                                                                       ##STR173##            H     H                                         C.sub.2 H.sub.5                                                                       ##STR174##            H     F                                         C.sub.2 H.sub.5                                                                       ##STR175##            F     F                                         n-C.sub.3 H.sub.7                                                                     ##STR176##            H     H                                         n-C.sub.3 H.sub.7                                                                     ##STR177##            H     F                                         n-C.sub.3 H.sub.7                                                                     ##STR178##            F     F                                         n-C.sub.5 H.sub.11                                                                    ##STR179##            H     H                                         n-C.sub.5 H.sub.11                                                                    ##STR180##            H     F                                         n-C.sub.5 H.sub.11                                                                    ##STR181##            F     F                                         n-C.sub.3 H.sub.7                                                                     ##STR182##            H     H                                         n-C.sub.3 H.sub.7                                                                     ##STR183##            H     F                                         n-C.sub.3 H.sub.7                                                                     ##STR184##            F     F                                         n-C.sub.5 H.sub.11                                                                    ##STR185##            H     H                                         n-C.sub.5 H.sub.11                                                                    ##STR186##            H     F                                         n-C.sub.5 H.sub.11                                                                    ##STR187##            F     F                                         C.sub.2 H.sub.5                                                                       ##STR188##            H     H                                         C.sub.2 H.sub.5                                                                       ##STR189##            H     F                                         C.sub.2 H.sub.5                                                                       ##STR190##            F     F                                         n-C.sub.3 H.sub.7                                                                     ##STR191##            H     H                                         n-C.sub.3 H.sub.7                                                                     ##STR192##            H     F                                         n-C.sub.3 H.sub.7                                                                     ##STR193##            F     F                                         n-C.sub.5 H.sub.11                                                                    ##STR194##            H     H                                         n-C.sub.5 H.sub.11                                                                    ##STR195##            H     F                                         n-C.sub.5 H.sub.11                                                                    ##STR196##            F     F                                         ______________________________________                                    

MIXTURE EXAMPLES EXAMPLE A

    ______________________________________                                        PCH-5F      9.50%      Clearing point [°C.]: 90.6                      PCH-6F      7.60%      Δn [589 nm, 20° C.]: 0.0975               PCH-7F      5.70%      Δε [1 kHz, 20° C.]: 6.11          CCP-2OCF.sub.3                                                                            7.60%                                                             CCP-3OCF.sub.3                                                                            11.40%                                                            CCP-4OCF.sub.3                                                                            8.55%                                                             CCP-5OCF.sub.3                                                                            8.55%                                                             BCH-3F.F    8.55%                                                             BCH-5F.F    11.40%                                                            ECCP-3OCF.sub.3                                                                           9.50%                                                             ECCP-5OCF.sub.3                                                                           4.75%                                                             CBC-33F     1.90%                                                             CBC-53F     1.90%                                                             CBC-55F     1.90%                                                             CUU-5-OMT   5.00%                                                             ______________________________________                                    

EXAMPLE B

    ______________________________________                                        PCH-5F      9.50%      Clearing point [°C.]: 89%                       PCH-6F      7.60%      Δn [589 nm, 20° C.]: 0.0968               PCH-7F      5.70%      Δε [1 kHz, 20° C.]: 6.05          CCP-2OCF.sub.3                                                                            7.60%                                                             CCP-3OCF.sub.3                                                                            11.40%                                                            CCP-4OCF.sub.3                                                                            8.55%                                                             CCP-5OCF.sub.3                                                                            8.55%                                                             BCH-3F.F    8.55%                                                             BCH-5F.F    11.40%                                                            ECCP-3OCF.sub.3                                                                           9.50%                                                             ECCP-5OCF.sub.3                                                                           4.75%                                                             CBC-33F     1.90%                                                             CBC-53F     1.90%                                                             CBC-55F     1.90%                                                             CUU-3-OMT   5.00%                                                             ______________________________________                                    

EXAMPLE C

    ______________________________________                                        PCH-5F      9.0%       Clearing point [°C.]: 83.9                      PCH-6F      7.2%       Δn [589 nm, 20° C.]: 0.0906               PCH-7F      5.4%       Δε [1 kHz, 20° C.]: 5.42          CCP-2OCF.sub.3                                                                            7.2%                                                              CCP-3OCF.sub.3                                                                            10.8%                                                             CCP-4OCF.sub.3                                                                            8.1%                                                              CCP-5OCF.sub.3                                                                            8.1%                                                              BCH-3F.F    10.8%                                                             BCH-5F.F    9.0%                                                              ECCP-3OCF.sub.3                                                                           4.5%                                                              ECCP-5OCF.sub.3                                                                           4.5%                                                              CBC-33F     1.8%                                                              CBC-53F     1.8%                                                              CBC-55F     1.8%                                                              CC-3-OMT    10.0%                                                             ______________________________________                                    

We claim:
 1. A 1,2,2,2-Tetrafluoroethyl ether of formula I

    R--(A.sup.1 --Z.sup.1).sub.m --A.sup.2 --Z.sup.2 --A.sup.3 --O--CHF--CF.sub.3                                        I

in which R is H, an alkyl or alkenyl radical having 1 to 15 carbon atomswhich is unsubstituted, monosubstituted by CN or CF₃ or at leastmonosubstituted by halogen, and one or more CH₂ groups in these radicalsis optionally replaced, in each case independently of one another, by--O--, --S--, ##STR197## --CO--, --CO--O--, --O--CO-- or --O--CO--O-- insuch a way that O atoms are not linked directly to one another, A¹, A²and A³ are each, independently of one another,(a) atrans-1,4-cyclohexylene radical in which, in addition, one or morenon-adjacent CH₂ groups is optionally replaced by --O-- and/or --S--,(b) a 1,4-phenylene radical in which, in addition, one or two CH groupsis optionally replaced by N, (c) a radical from the group consisting of1,4-cyclohexenylene, 1,4-bicyclo[2.2.2.]octylene, piperidine-1,4-diyl,naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl and1,2,3,4-tetrahydronaphthalene-2,6-diyl,where the radicals (a) and (b)are optionally substituted by one or two fluorine atoms, Z¹ and Z² areeach, independently of one another, --CO--O--, --O--CO--, --CH₂ O--,--OCH₂ --CH₂ CH₂ --, --CH═CH--, --C.tbd.C-- or a single bond, one of theradicals Z¹ and Z² also being --(CH₂)₄ -- or --CH═CH--CH₂ CH₂ --, and mis 0,1 or
 2. 2. A compound according to claim 1, of formula I'##STR198## in which L² is H or F.
 3. A compound according to claim 1, offormula I1 ##STR199## in which L¹ and L² are each, independently of oneanother, H or F.
 4. A compound according to claim 1, of formula I3##STR200## in which L¹ and L² are each, independently of one another, Hor F.
 5. A compound according to claim 1, of formula I12 ##STR201##
 6. Acompound according to claim 1, of the formula ##STR202## in which L² isH or F.
 7. A compound according to claim 1, of the formula ##STR203## inwhich L² is H or F.
 8. A process for the preparation of substituted1,2,2,2-tetraluoroethoxybenzene from the corresponding phenoxide,comprising reacting the phenoxide with 1,2,2,2-tetrafluoro-1-iodoethanein the presence of an inert solvent.
 9. A process according to claim 8for the preparation of a 1,2,2,2-tetrafluoroethylphenyl ether of formulaIII* ##STR204## in which R* is halogen, formyl or a mesogenic group, andL¹ and L² are each, independently of one another, H or F, said processcomprising reacting a corresponding phenoxide with1,2,2,2-tetrafluoro-1-iodoethane in the presence of an inert solvent.10. A process according to claim 9, wherein the inert solvent used is apolar aprotic solvent.
 11. A process according to claims 9, wherein thesolvent used is an organic amide or a cyclic urea derivative.
 12. Aprocess according to claim 11, wherein the solvent used is1,3-dimethyl-2-imidazolidinone (DMEU).
 13. A liquid-crystal mediumcomprising at least two liquid-crystalline components, wherein at leastone component is at least one compound of formula I of claim
 1. 14. Aliquid-crystal display element, containing a liquid-crystalline mediumaccording to claim
 13. 15. In a method for producing an electro-opticaldisplay using a dielectric, the improvement wherein the dielectriccontains a liquid-crystalline medium according to claim 13.